I tried the synthetic stuff for my hypothyroid issues and just could not deal with it. All my endo would prescribe was the synthetic crap so I took matters into my own hands and found some natural dessicated thyroid on the Internet.
Get your hands on a book called Stop the Thyroid Madness.
Lots of info and reference material in it. They also have a website by the same name with most all the same information.
Best wishes to you and your Baby.